99% of my spending is via debit, but I always have cash as well.

day to day, I usually have no less than $200. on me, generally in $20's

Travelling, depending on where...
in remote back country Canada - I usually up it to $400, generally in $20's.
in the US, I will generally carry $100./day that I plan on being there, but I'll spend credit/debit.

Foreign...
depends on where, In the Caymans, I doubled what I carry in the US because everything was twice as expensive.
in Columbia, I kept $20. on me, in $1.00's, plus a handful of change.